Staged calcining of fluid coke with falling, non-fluid bed



Nov. 5, 1957 STAGED CALCINING c. N. KIMBERLIN, JR 2,812,289

0F FLUID COKE WITH FALLING, NON-FLUID BED Filed May 24, 1955 F ll 7FALLING, NON-FLUID BED OF COKE COKE WITHDRAWAL Charles N. Kimberh'r JrInvenfbr By C Attorney United States Patent STAGED CALCINING 0F FLUIDCOKE WITH FALLING, NON -FLUID BED Charles Newton Kimberlin, Jr., BatonRouge, La., as-

signor to Esso Research and Engineering Company, a corporation ofDelaware Application May 24, 1955, Serial No. 510,693

Claims. (Cl. 20231) This invention relates to improvements in thedesulfurization, devolatilization and increase in electricalconductivity of fluid coke. More particularly it relates to a stagedcalcining treatment wherein the coke is treated While in the form of afalling, non-fluid bed. The coke is first contacted with a gaseoushydrocarbon at a lower temperature and the evolved hydrogen furthertreats the coke at a higher temperature.

There has recently been developed an improved process known as the fluidcoking process for the production of fluid coke and the terminalconversion of heavy hydrocarbon oils to lighter fractions, e. g., seeSerial No. 375,088, filed August 10, 1953. For completeness the processis described in further detail below although it should be understoodthat the fluid coking process itself is no part of this invention.

The fluid coking unit consists basically of a reaction vessel or cokerand a heater or burner vessel. In a typi- .cal operation the heavy oilto be processed is injected into the reaction vessel containing a dense,turbulent, fluidized bed of hot inert solid particles, preferably cokeparticles. A transfer line or staged reactors can be employed. Uniformtemperature exists in the coking bed. Uniform mixing in the bed resultsin virtually isothermal conditions and effects instantaneousdistribution of the feed stock. In the reaction zone the feed stock ispartially vaporized and partially cracked. Product vapors are removedfrom 1.

the coking vessel and sent to a fractionator for the recovery of gas andlight distillates therefrom. Any heavy bottoms is usually returned tothe coking vessel. The coke produced in the process remains in the bedcoated on the solid particles. Stripping steam is injected into thestripper to remove oil from the coke particles prior to the passage ofthe coke to the burner.

The heat for carrying out the endothermic coking reaction is generatedin the burner vessel, usually but not necessarily separate. A stream ofcoke is thus transferred from the reactor to the burner vessel, such asa transfer line or fluid bed burner, employing a standpipe and risersystem; air being supplied to the riser for conveying the solids to theburner. Sufficient coke or added carbonaceous matter is burned in theburning vessel to bring the coke production, which represents the cokemake less the coke burned, is withdrawn.

Heavy hydrocarbon oil feeds suitable for the coking process includeheavy crudes, atmospheric and crude vacuum bottoms, pitch, asphalt,other heavy hydrocarbon petroleum residua or mixtures thereof. Typicallysuch feeds can have an initial boiling point of about 700 F.

or higher, an A. .P. I. gravity of about 0 to 20, and a Conradson carbonresidue content of about 5 to 40 wt.

2,812,289 Patented Nov. 5, 1957 above 6 wt. percent, and a volatilecontent of 2 to 10 wt.

percent. They have a real density of about 1.4 to 1.7 which is too lowfor use in the manufacture of carbon electrodes for making aluminum andother purposes. Increased density and lower sulfur and volatile contentare particularly necessary before the fluid coke is suitable formanufacture into electrodes, one of the major uses of petroleum coke.The attainment of these properties can be accomplished by calcining thecoke at high temperatures, e. g., minimum temperatures of 2100 F. orhigher. These temperatures and the times required make the calciningoperation relatively diflicult and expensive. It is therefore desirableto effect improvements in the calcination and conditioning of the fluidcoke.

This invention provides an improved staged calcining operation forachieving this purpose. The process comprises treating the coke in aunitary calcining zone while in the form ot a falling, non-flud bed. Anormally gaseous hydrocarbon countercurrently contacts the fluid coke ina lower portion of the calcination zone at a temperature in the range ofl800 to 2200 F. The hydrocarbon is cracked to hydrogen and carbon whichlatter deposits in the voids of the fluid coke. The evolved hydrogencountercurrently contacts the falling fluid coke in an upper portion ofthe calcination zone at a temperature in the range of 2000 to 2.700" P.

The total holdup time in the calcination zone is in the range of about30 minutes to 6 hours. The temperature in the lower part of the bed islow because of the endothermic heat of the cracking reaction occurringtherein. In passing form the bottom to the top of the bed there is firsta fairly rapid increase in temperature and thereafter a less rapidincrease. The size of the zone of rapid temperature change (which is thezone Where most of the cracking is occurring) will depend upon the rateof flow of gas, i. e., for a high rate of flow this zone will be largerthan for a low rate of flow. This zone will ordinarily occupyone-t-entlrto one-half, preferably about onefourth, of the total bedvolume. The time of high temperature treating can thus be in the rangeof 20 minutes to four hours and the lower temperature in the range of 10minutes to two hours.

The falling, non-fluid bed is that the same as a moving bed. Theparticles are substantially not in motion with respect to each other,but the total mass slowly descends through the vessel. The rate ofdescent is in the range of 1 to ft./ hr. depending upon the design ofthe vessel and upon the contact or residence time desired. The densityof the bed is about 55 to 62 lbs/cu. ft.

The velocity of the treating gases, i. e., the evolved hydrogen and thenormally gaseous hydrocarbon, is thus kept below that required tofluidize the coke. The linear velocity is the critical one and should bekept below a maximum of about 0.2 ft./sec., preferably about 0.1 ft./sec. or less. This does not depend upon vessel geometry.

The normally gaseous hydrocarbons that can be employed include C1 to C4hydrocarbons such as methane, ethane, propane and butane. Unsaturatessuch as ethylene, propylene, butylene can also be employed. Methane isparticularly preferred and effective. The gas rate as expressed involumes of gas per volume of coke per hour '2800 F. e. g. 2700 F. tosupply the heat requirements further downstream in the process. Atransfer line burner can be used if desired. This heating isaccomplished by burning part of the coke with preheated air from line 5.If desired an alternative fuel such as gas or oil from line 7 may beburned to supply the heat.

Flue gases are vented through cyclone 8 and line 10.

Solids are returned to the bed through dipleg 12.

The heated coke is transferred by line 9 into an upper "portion ofcalcination zone 11, preferably conical shaped,

to provide easy passage of the dense bed. In the upper zone 20 ofcalciner 11 the falling, non-fluidized fluid coke .particles are treatedwith hydrogen at a temperature in the range of 2000 to 2700 F., e. g.2600 F. The temperature at the very top of zone 20 will be the same asthat of the entering coke, i. e. 2700 F. in the example.

However, the temperature in the lower part of this zone will beconsiderably lower, say about 2200 to 2400 F.

4 sisting essentially of hydrogen as the treating gas. The coke wastreated for minutes with'hydrogen at each temperature as shown in TableI.

Table I HYDROGEN OALCINATION OF FLUID GOKE EFFEOT OF TEMPERATURE(30.-MINUTE TREATMENT) Coke Sulfur, Real Temp., F. Yield, Wt. Density,

Wt. Percent 25 0. Percent 1! Original green coke contained 7.5 wt.percent sulfur and had a density of 1.50 at 25 C It is apparent from thedata in Table I that temperatures of 2000 F. and above are required togeta good rate of sulfur removal.

EXAMPLE 2 Direct comparisons were made between gases consistingessentially of hydrogen and several other common gases in fluid cokecalcining at 2400 F. and 2700 F. The coke was treated for 30 minuteswith the various gases, all at the same v./v./hr. Summary data are givenin Table II.

Table II COMPARISON OF HYDROGEN WITH OTHER COMMON GASES IN'FLUID COKEOALCINING (30 Minute Treatment) Steam (75 vol.

Treating Gas Hg Hz N a N2 Air Air Steam C0 C02 CH percent), C0

(25 vol. percent) Temperature, F 2, 400 2, 700 2, 400 2, 700 2, 400 2,700 2, 400 2, 400 2, 400 2, 400 2, 400 Coke Yield, Wt. Percent 89 83 9285 90 80 97 1 80 Sulfur, Wt. Percent 4. 9 l. 8 7. 4 3. 7 6. 7 2. 8 a 5.2' 6. 2 5. 8 n 5. 6 5. 7

Original green coke contained 7.5 wt. percent sulfur.

b Yields not available for these runs.

s Yield high because of carbon deposition from OH; cracking.

is needed to heat up the hydrogen from the cracked gases entering below,and (2) heat is consumed in vaporizing the volatile matter of the cokeincluding the sulfur. The hydrogen which has been evolved in a lowerzone 22 and which thus countercurrently treats the fluid coke in upperzone 20 is at a linear velocity insufficient to fluidize the coke, lessthan about 0.2 ft./sec.', e. g. 0.1 ft./sec. The hydrogen, hydrogensulfide, carbon disulfide and other volatiles are removed through line13.

-e. g. 2100 F. The density and electrical conductivity of the coke isincreased. The residence time in the upper zone 20 is 1 /2 hours and inthe lower zone 22 is /2 hour.

The desulfurized coke is with-drawn from a lower portion of the calcinerthrough line 17.

The particular advantage of hydrogen at elevated temperature in thetreatment of fluid'coke is demonstrated in'the following examples.

EXAMPLE 1 .Inone series of runs the temperature of calcination wasvaried from 1350 to 2700 F. while using a gas con- The temperature dropcomes about in two ways: (1) heat Methane gives high coke yields for agivenreduction in sulfur content. Although yield values are now shown inTable II for air and steam, these gases are known to consume cokerapidly at these temperatures. This fact is more apparentat longercontact times.

Yields are lower for air and steam-because-both attack the carbon.Oxygen in the air burns the coke to give CO and steam gives CO+H2 by thewater gas'reaction. As an illustration, one run made with air at 4500v./v./hr. at 2400 F. and for a time of 20' minutes gave a yield of 82.5%as compared with 89% for hydrogen at a time of 30 minutes.

Another air run made at 2700 F. gave a yield of only 74.0% using a 20minute'time of treating.

It is important to note the advantage for hydrogen over all the othergases shownin sulfur content. of the coke product. Thisholds for both2400 F. and 2700 F, The superiority for hydrogen overnitrogen issignificant in view of the fact that both are inert gases insofar as anyreactionwith the carbon of the coke is concerned.

These runs were discontinued for the most part after 30 minutes becausetime intervals of that nature have been found to be valid and reliableinscreening tests on different gaseous materials. Varying thetcrnperatureor time of treatment of both within the prescribed rangescan bring the sulfur content down to levels required.

The advantages of the process of this invention reside particularly inthe fact that in addition to the desulfurization that is obtained, acoke product of high density, purity and good conductivity is providedwithout requiring an extraneous hydrogen supply.

The sulfur content of thecoke canbe reduced to be- CONDITIONS IN FLUIDCOKER REACTOR Broad Preferred Range Range Temperature, F 850-1. 200900-1. 000 Pressure, Atmospheres -1- l-lO 1. 5-2 Superficial Velocity ofFluidizing Gas, cc. 0. 2-10 0. 5-4 Coke Circulation (Solids/Oil Ratio)2-30 7-15 It is to be understood that this invention is not limited tothe specific examples which have been otfered merely as illustrationsand that modification may be made without departing from the spirit ofthe invention.

What is claimed is:

1. A process for desulfurizing, devolatilizing and increasing thedensity of fluid coke particles which comprises the steps of feedingheated coke particles to an upper portion of a calcination zone;maintaining the coke particles therein in the form of a falling,non-fluid bed; countercurrently contacting the coke particles underreducing conditions in an upper portion of the calcination zone at atemperature in the range of 2000 t0 2700 F. with hydrogen evolved in thelower portion of the calcination zone, the hydrogen velocity being lessthan that required to fiuidize the coke; countercurrently contacting thethus treated coke in a lower portion of the calcination zone at atemperature in the range of 1800 to 2200" E. with a normally gaseoushydrocarbon at a velocity less than that required to fiuidize the coke,the hydrocarbon being cracked to hydrogen and carbon which deposits onthe voids of the fluid coke, said cracking cooling the coke to therequired temperature and withdrawing calcined fluid coke product fromthe lower portion of the calcination zone, the total treating time inthe calcination zone being in the range of minutes to 6 hours.

2. The process of claim 1 in which the treating time in the upper zoneis in the range of 20 minutes to 4 hours, and the treating time in thelower .zone is in the range of 10 minutes to 2 hours.

3. The process of claim 1 in which the maximum linear velocity of thehydrogen and the normally gaseous hydrocarbon is 0.2 ft./sec.

4. The process of claim 3 in which the normally gaseous hydrocarbon isutilized in an amount of 20-150 v./v./hr. and the density of thefalling, non-fluid bed is in the range of -62 lbs/cu. ft.

5. The process of claim 4 in which the normally gaseous hydrocarbon ismethane.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PSROCESS FOR DESULFURIZING, DEVOLATILIZING AND INCREASING THEDENSITY OF FLUID COKE PARTICLES WHICH COMPRISES THE STEPS OF FEEDINGHEATED COKE PARTICLES TO AN UPPER PORTION OF A CLACINATION ZONE;MAINTAINING THE COKE PARTICLES THEREIN IN THE FORM OF A FALLING,NON-FLUID BED; COUNTERCURRENTLY CONTACTING THE COKE PARTICLES UNDERREDUCING CONDITIONS IN AN UPPER PORTION OF THE CALCINATION ZONE AT ATEMPERATURE IN THE RANGE OF 2000* TO 2700* F. WITH HYDROGEN EVOLVED INTHE LOWER PORTION OF THE CALCINATION ZONE, THE HYDROGEN VELOCITY BEINGLESS THAN THAT REQUIRED TO FLUIDIZE THE COKE; COUNTERCURENTLY CONTACTINGTHE THUS TREATED COKE IN A LOWER PORTION OF THE CALCINATION ZONE AT ATEMPERATURE IN THE RANGE OF 1800* TO 2200* F. WITH A NORMALLY GASEOUSHYDROCARBON AT A VELOCITY LES THAN THAT REQUIRED TO FLUIDIZE THE COKE,THE HYDROCARBON BEING CRACKED TO HYDROGEN AND CARBON WHICH DEPOSITS ONSTHE VOIDS OF THE FLUID COKE, SAID CRACKING COOLING THE COKE TO THEREQUIRED TEMPERATURE AND WITHDRAWING CALCINED FLUID COKE PRODUCT FROMTHE LOWER PORTION OF THE CALCINATION ZONE, THE TOTAL TREATING TIME INTHE CIRCINATION ZONE BEING IN THE RANGE OF 30 MINUTES TO 6 HOURS.